I often get wrong answers from the assistant in Shopify.dev. Is there a better way to get solutions?

I want to programmatically update the meta tags for all my products. But it’s been a pain to figure out how to do it using the new GraphQL API.

Well keep in mind the dev assistant will work based on whatever prompt you give it but it’s not perfect.
It might be a good idea to take a step back and review the GraphQL API docs for Product and see what kind of fields you need.
If I were you I’d spin up a simple custom Shopify App (literally one file in your language of choice) and play around with different GraphQL queries until you get the exact data you need.

Shopify has a pretty starter series on GraphQL on the ShopifyDevs YouTube channel.